Acoustic Treatments, 2" inches or 4" inches thickness?

[Techlord]

the rockwool/owens corning should do well in the upper frequencies, they're used for broadband absorption.

Which one is the better of the two?

Regards,
Techlord.

 

[mike c]

as long as the density is the same, they'll perform exactly the same.

i'm guessing your follow up question would be about which density is best for mid-high frequencies.

my advice is still to get the the highest density available to address a "broader" band of frequencies (hence the term broadband panel)

 

[Techlord]

as long as the density is the same, they'll perform exactly the same.

i'm guessing your follow up question would be about which density is best for mid-high frequencies.

my advice is still to get the the highest density available to address a "broader" band of frequencies (hence the term broadband panel)

It seems like Rockboard 60 is the material to go with, I'll have to put two 2" sheets together to make the 4" thick panel. What should I do to make the two 2" Rockwool stick together?

Thanks,
Techlord.

 

[highfigh]

The acoustics in my room were/are not bad to begin with. As I was able to build the room from scratch (started with bare basement - concrete walls and floor and joists), I could also build it with the fewest acoustical issues but altering my dimentions. I actually used an excel spreadsheet from Sound and Vision that calculated standing waves, nulls, and other acoustical issues based on room dimensions. I must have played with that spreadsheet for a week.

That said, my panels were built for moderate, but broad spectrum, absorption. So as quoted "Depends on the need." Mostly to handle first order reflections and decrease some of the bi-polar effect of my Def Tech speakers (reflections from the back of the speaker off the front wall were making it difficult to sometime clearly understand dialogue).

You can't design a room for sound, based purely on calculations. At some point, the response will have to be measured. The speakers will determine what you need because of their polar response, which you have already noticed. Pink noise, fast sweeps and impulse need to be used.

 

[Bryce_H]

Agreed and I will get there, but the fact I could play with my room dimentions helped a lot from the start. I wil get to the point of getting the sweeps, etc. completed.

 

[lsiberian]

as long as the rockwool and owens corning have the same density, they have the same effect.

that said, get the highest density available to you.

http://www.bobgolds.com/AbsorptionCoefficients.htm is a good list to go off of.

Anything 0.85 or better is considered 100 percent. You'll find a correlation with density isn't always there, but thickness always improves LFE absorption.

 

[Techlord]

http://www.bobgolds.com/AbsorptionCoefficients.htm is a good list to go off of.

Anything 0.85 or better is considered 100 percent. You'll find a correlation with density isn't always there, but thickness always improves LFE absorption.

At what point do mid-range and high frequencies get absorbed using Rockboard 60 4" thick?

Regards,
Techlord.

 

[highfigh]

At what point do mid-range and high frequencies get absorbed using Rockboard 60 4" thick?

Regards,
Techlord.

Any thickness of absorptive material will be more efficient at mid and higher frequencies than low unless that panel is made to resonate (diaphragm) or it's tuned (like a Helmholtz resonator). If you go to any manufacturer's site for a particular material, you'll see STC and NRC charts. Midrange is one area that can benefit from using a thinner panel and providing an air space behind it- some sound will pass through because it's porous and the vast majority of whatever reflects after hitting the wall will be absorbed when it hits the back of the panel.

 

[nibhaz]

the higher the density, the more low frequencies it can catch.

http://www.bobgolds.com/AbsorptionCoefficients.htm is a good list to go off of.

Anything 0.85 or better is considered 100 percent. You'll find a correlation with density isn't always there, but thickness always improves LFE absorption.

Density and low end absorption are not directly related per se. In fact density is just a metric commonly used to guesstimate gas flow resistivity, which is not a commonly published property.

The statement that higher density equals more low in absorption, is generally true for thinner panels in the 2” to 4” range, and but when you start talking about really thick absorbers >8”, or filled corners, you will actually get better performance over a broader range of frequencies with a less dense material, which is rather counterintuitive.

Denser materials do absorb slightly better at the lowest octaves, but their rate of abortion in relation to frequency is very linear in comparison to less dense materials which tend to reach high rates of absorption rather abruptly.


If you look at the following simulations of 9” panels you’ll see what I mean.


701


703


705


The 705 panel does have the highest abortion rate at 20 Hz but sacrifices a lot of abortion in the mid-bass region.

 

[Techlord]

Density and low end absorption are not directly related per se. In fact density is just a metric commonly used to guesstimate gas flow resistivity, which is not a commonly published property.

The statement that higher density equals more low in absorption, is generally true for thinner panels in the 2” to 4” range, and but when you start talking about really thick absorbers >8”, or filled corners, you will actually get better performance over a broader range of frequencies with a less dense material, which is rather counterintuitive.

Denser materials do absorb slightly better at the lowest octaves, but their rate of abortion in relation to frequency is very linear in comparison to less dense materials which tend to reach high rates of absorption rather abruptly.


If you look at the following simulations of 9” panels you’ll see what I mean.


701


703


705


The 705 panel does have the highest abortion rate at 20 Hz but sacrifices a lot of abortion in the mid-bass region.

My goal is to stop the "Slap Echo" in the mid-range and high frequency, I had a friend over lastnight and we could clearly hear the the same sound image arive at different times especially nearer in the corners of the room.

Thanks for the graphs,

Techlord.

 

[Techlord]

Any thickness of absorptive material will be more efficient at mid and higher frequencies than low unless that panel is made to resonate (diaphragm) or it's tuned (like a Helmholtz resonator). If you go to any manufacturer's site for a particular material, you'll see STC and NRC charts. Midrange is one area that can benefit from using a thinner panel and providing an air space behind it- some sound will pass through because it's porous and the vast majority of whatever reflects after hitting the wall will be absorbed when it hits the back of the panel.

I am planning on having 4" of Rockboard 60 with a gap behind the frame of about 2" or less. Can mid-range and high frequncies actually pass through 4" of Rockboard?

Regards,
Techlord.

 

[highfigh]

I am planning on having 4" of Rockboard 60 with a gap behind the frame of about 2" or less. Can mid-range and high frequncies actually pass through 4" of Rockboard?

Regards,
Techlord.

At 4", it will be pretty well attenuated by the time it gets to the backside. for highs, 1" works well and when I did a theater demo room for the company I worked for in '93, they didn't want the treatments to be extremely thick, so I could only go with 2" in some areas and 1" in the rest. The room wasn't very wide and flutter was really bad but with the panels, it was only slightly audible at high SPL and extremely short duration transients.

I used Owens-Corning 703 that time and recently, when I bought a bundle to make some panels to demonstrate the effects (I didn't want to wait for Roxul). When I don't need to move them, I'm using them in my room and the difference is very obvious when they're gone. I made one panel 4" thick and the rest are 2". Four panels are 1'x3'x2" and the rest are 2'x4'.

The sheets can be joined using contact cement along the edges and through the center.

 

[Techlord]

At 4", it will be pretty well attenuated by the time it gets to the backside. for highs, 1" works well and when I did a theater demo room for the company I worked for in '93, they didn't want the treatments to be extremely thick, so I could only go with 2" in some areas and 1" in the rest. The room wasn't very wide and flutter was really bad but with the panels, it was only slightly audible at high SPL and extremely short duration transients.

I used Owens-Corning 703 that time and recently, when I bought a bundle to make some panels to demonstrate the effects (I didn't want to wait for Roxul). When I don't need to move them, I'm using them in my room and the difference is very obvious when they're gone. I made one panel 4" thick and the rest are 2". Four panels are 1'x3'x2" and the rest are 2'x4'.

The sheets can be joined using contact cement along the edges and through the center.

Are you saying 4" inches is too thick? What is flutter? I want to eliminate the Slap Echo and all of the high frequencies from bouncing around thr room.

Regards,
Techlord.

 

[lsiberian]

I am planning on having 4" of Rockboard 60 with a gap behind the frame of about 2" or less. Can mid-range and high frequncies actually pass through 4" of Rockboard?

Regards,
Techlord.

Sound is pressure so it's not really passing through. It's absorption and broadband absorption behind the seating position prevent the sound from the mains from being bounced back at your ears from the rear wall. usually 2" is enough for most folks. 4" can look dreadful.

You can't optimize an entire room. you can only really optimize an area.

it's like if you got beat with a pillow versus a bat. The pillow is a much better absorber of the force than the bat.

 

[Techlord]

Now I am confused getting two different opinions that are opposite of each other, now I don't know what to do! Maybe I should just hang a carpet on the wall...

What materials are considered broadband absorption?

 

[highfigh]

Are you saying 4" inches is too thick? What is flutter? I want to eliminate the Slap Echo and all of the high frequencies from bouncing around thr room.

Regards,
Techlord.

If you're referring to repeats in quick succession when you clap your hands, that's also known as 'flutter'. Any descriptions I use are from what I read when I got into this about 30 years ago. Just don't treat me like I'm Abe Simpson, OK?

How thick the panels need to be is determined by how strong the reflections are. The absorption is determined by the material's NRC/unit, frequency, intensity and area of coverage. If you have the right dimensions, flutter will be really bad, like it was in the room I treated back in '93. It was my first time, although I had dealt with the principles and theories when I was in school. The books I have from school have basically the same info as what's available now and fortunately, my calculations worked, although it would have been much easier with a computer.

If you look at the graphs, you see that the effect rolls off as the frequency drops. If you double the thickness, the effect is additive but what will be needed is determined by the actual measurements. There's no point in trying to make a room do what you want when it just won't.

Get some materials and play around with them. I used muslin to cover mine because it holds the fibers in but breathes well, so the fiberglass still gets the full sound to absorb. I backed mine with pegboard and I turned the one behind me so the pegboard side is facing my speakers. It still absorbs but not as much as if the fiberglass was facing them. If you put your ear close to a highly absorptive material, it's kind of unpleasant.

 

[highfigh]

Sound is pressure so it's not really passing through. It's absorption and broadband absorption behind the seating position prevent the sound from the mains from being bounced back at your ears from the rear wall. usually 2" is enough for most folks. 4" can look dreadful.

You can't optimize an entire room. you can only really optimize an area.

it's like if you got beat with a pillow versus a bat. The pillow is a much better absorber of the force than the bat.

But the molecular motion does mean the pressure wave enters the material. Once it hits a boundary, it stops and that's a point of high pressure but zero velocity. When the energy is absorbed by the surface or a material that can cause the motion to slow greatly, it has to change from one form to another, which is heat. If the pressure wasn't passing through, you wouldn't be able to hear the sound on the other side but you will hear the filtered sound if you place a sheet of 703 between you and a sound source. It reduces the sound at the rate it can and when the panel has a gap, it reflects, hits the panel again and more energy is lost in the range where the material is best able to absorb it.

One thing to make 4" of material look better is to flank it with thinner panels and make it a feature of the room. Also, 4" thickness looks a lot worse in a small room.

 

[mike c]

Now I am confused getting two different opinions that are opposite of each other, now I don't know what to do! Maybe I should just hang a carpet on the wall...

What materials are considered broadband absorption?

exactly why normal people don't need to know too much information. [me included]

the differences are just plain too negligible to matter.

personally, i'd still go with the higher density. it's easy enough to deal with the higher frequencies than the low ones.

 

[Techlord]

exactly why normal people don't need to know too much information. [me included]

the differences are just plain too negligible to matter.

personally, i'd still go with the higher density. it's easy enough to deal with the higher frequencies than the low ones.

I guess I'm suffering from information overload, more confused now then when I started! I just want to hang some sound absorbing materials and play around with room placement, then be done with it. Please do not make this too technical (molecular motion, please..) as in keep it simply, listing some excellent materials and thinknesses would be most helpful.

Thank you,
Techlord.

 

[nibhaz]

I guess I'm suffering from information overload, more confused now then when I started! I just want to hang some sound absorbing materials and play around with room placement, then be done with it. Please do not make this too technical (molecular motion, please..) as in keep it simply, listing some excellent materials and thinknesses would be most helpful.

Thank you,
Techlord.

Okay, let’s keep it real simple.

Assuming you only want to tackle flutter echo:

You want 2” panels of 3lbs/ft^3 fiberglass (OC 703) or 6lbs/ft^3 Rockwool. If you find that you need more performance in the lower frequencies add a 2” air gap behind the panels. Rockwool will be the cheapest option and 705 is just a little too expensive when considering the slight performance gain in my opinion.

2” Panel 705



2” Panel 703



2” Panel 701